stoma n.

in anatomy, "union or intercommunication of the vessels of one system with those of another," 1610s, medical Latin, from Greek anastomosis "outlet, opening," from anastomoein "to open, discharge" (as one sea into another), "to furnish with a mouth," from ana "again, anew" (see ana-) + stoma "mouth" (see stoma). Related: Anastomotic.

1888, from combining form of colon (n.2) + Modern Latin -stoma "opening, orifice," from Greek stoma "opening, mouth" (see stoma). Colotomy "operation of making an incision in the colon" is attested from 1860, from Greek tome "a cutting."